The present invention relates to an electronic switching device for an antenna switchable in the VHF and UHF frequency ranges, for example 100 to 156 MHz for the VHF range and 225 to 400 MHz for the UHF range.
Such antennas are often, but not exclusively, used on board civil or military aircraft.
In the reference FR-A 2 552 587 (which corresponds to U.S. Pat. No. 4,656,483 in the name of Herve JAQUET) there is described a switchable antenna which comprises a capacitive element spaced from a flat reflector forming the ground, a first self-inductance located between the capacitive element and a feed through the flat reflector, and connected to a transmitter-receiver, this first self-inductance being formed from several sections, each associated with a switch which enables certain sections to be short-circuited at will for operation in the VHF range and all sections for operation in the UHF range. The antenna described in this reference further comprises a second self-inductance which can be connected by a switch between the first self-inductance and the ground plane in the VHF range and disconnected in the UHF range, as well as conductive sleeves inserted between the capacitive element and the ground plane, on either side of the self-inductances.
The switches associated with the sections of the first self-inductance and with the second self-inductance advantageously comprise PIN diodes. In conventional manner bias voltages for controlling the bias of these diodes are injected by means of conductors which feed through the ground plane and in which high-frequency isolating self-inductances are provided.
This arrangement, as applied to antennas, has several disadvantages:
perturbations in the response of the antenna due to the proximity of the conductive wire, PA1 limited frequency bandwidth of the switch, because this is dependent on the impedance of the self-inductance for blocking high-frequency voltages PA1 inadequate resistance of the self-inductances to large high-frequency over-voltages, if they comprise a ferrite core, PA1 loss of output caused by the blocking self-inductances, PA1 risk of introducing radio interference below the surface of the support vehicle of the antenna by way of the conductive bias wires.
In order to limit these problems it is proposed in the document cited at the beginning of this specification to protect the conductors transmitting the bias voltages for the diodes by making them pass coaxially to the inside of conductors of certain parts of the self-inductance, formed by a metal tube wound in a spiral,. This ingenious solution does not completely avoid the recited problems because the protection of these conductors is not complete, in particular between the self-inductance and the passages through the ground plane.
The object of the present invention is to provide a switching device which does not have the above disadvantages or only exhibits them in a greatly reduced manner compared with the prior art.